Li2(NH2BH3)(BH4)/LiNH2BH3: The first metal amidoborane borohydride complex with inseparable amidoborane precursor for hydrogen storage

A novel lithium amidoborane borohydride complex, Li2(NH2BH3)(BH4), was synthesized using mechanochemical method and its crystal structure was successfully determined by a combination of X-ray diffraction (XRD) analysis and first-principles calculations. Interestingly, this compound does not exist as a pure phase, but requires almost equivalent amount of amorphous LiAB as a stabilizing agent. In this paper, we report a careful study of the structure, property, and dehydrogenation mechanism of the 1:1 Li2(NH2BH3)(BH4)/LiAB composite. This composite can release ∼8 wt% H2 at 100 °C via a two-step dehydrogenation process, with dehydrogenation kinetics better than the parenting phases. The composite and its dehydrogenation products were characterized by the combined XRD, Fourier transformation infrared (FTIR) spectroscopy, and solid-state 11B MAS NMR techniques. Selective deuterium labeling was performed to elucidate a reaction sequence for the hydrogen release by analyzing the released gases.

► A new lithium amidoborane borohydride complex, Li2(NH2BH3)(BH4), is synthesized. ► The crystal structure of Li2(NH2BH3)(BH4) is successfully determined. ► The 1:1 Li2(NH2BH3)(BH4)/LiAB composite exhibits improved DH kinetics than LiAB. ► The reaction sequence of H2 release from this composite is determined. ► The mechanism for the improvement of the DH kinetics is discussed.